The present invention relates to electric tools having lighting devices, and in particular, to portable electric drills and screwdrivers having lighting devices. Such lighting devices permit the operator to illuminate the working area in accordance with ambient light levels. The present invention also relates to lighting devices that can be utilized, for example, in machine tools.
German Patent No. 3831344 discloses a portable drill having a lighting device comprising a plurality of light emitting diodes (LEDs), which are suitable to illuminate the working area. These LEDs are powered and controlled by the same electric power supply and motor control means of the machine tool.
However, when the ambient light intensity is high, the light from the lighting device may be too bright and may possibly stun the operator if the operator looks into the light. Further, if lighting device shines even though the ambient light intensity is already sufficient to light the work area, energy will be wasted, which is disadvantageous for battery powered tools.
Therefore, it is an object of the present invention is to provide a lighting device that overcomes these problems and can be utilized in power tools, and in particular in portable drills and screwdrivers.
In one aspect of the present teachings, a power tool is taught that has a light adapted to illuminate a work area, an ambient light sensor and a controller adapted to change the intensity of the light based upon the ambient light conditions detected by the sensor. As a result, the controller can automatically turn the light on and off depending upon ambient light conditions. Further, the controller may also be adapted to adjust the intensity of the light based upon the ambient light conditions in an inversely proportional manner. Preferably, the light is supplied by light emitting diodes (LEDs).
The tool may further include circuits for improving the efficiency of the tool and to reduce the energy consumption of the tool. A delay circuit may be provided to delay turning off the light emitting diodes, so as to continue to illuminate the working area for a period of time after the motor of the power tool has stopped.
Due to its simplicity, the present teachings can be incorporated both into existing tools as well as into newly conceived power tools. Embodiments are taught that provide an advantageous shape for a printed circuit that holds the sensor and a printed circuit protection cap. In addition, a voltage limiting circuit is taught that permits the present teachings to be utilized with several different kinds of power tools, irrespective of the supply voltage.
Further advantages and features of the lighting device according to the present invention will be evident to those skilled in the art front the following detailed description of an embodiment thereof with reference to the attached drawings.